what causes leaves and stems on flowers to turn silver/frost?

Answer 1

cold & moisture combined, I think

Answer 2

From what I found that is the name of it Silver leaf. Here is some info A serious disease of Plum trees, which can also affect Apples, Cherries and Peaches. The leaves have a silver sheen on them turn brown and drop off the tree. Dieback of shoots occurs and when the wood is cut into, a black ring can be seen. Cut out all dead branches below the level of infection and paint all wounds with Arbrex. In extremely severe cases, toadstools will appear at the base of the tree. If this happens, the tree will have to be dug out and burned.

SILVER LEAF (FALSE)

This looks like silver leaf at first glance with all the leaves turning silver. If the wood is cut there will not be the distinctive black ring of true silver leaf. This is caused by a lack of water. Put down a thick mulch in spring and keep well watered.

Answer 3

it also could be powdery mildew. caused by too much moisture
Pull off an affected leaf.. place in ZIP LOCK baggie.. and take it to a greenhouse.. not a supermarket.. but a real greenhouse or reputable lawn care professional. Dont go spreading your diseased leaves around. The people at the greenhouse dont want thier plants affected too.